With the continuous development of multimedia devices, the organic light emitting diode (OLED) has been increasingly used in high performance displays. In order to be adapted to large display size, a shorter driving time for a single pixel is required for a traditional passive matrix OLED. Therefore, an increased transient current is needed, resulting in increased power consumption. At the same time, the use of large current may lead to a too large voltage drop in a pixel array, so that the operation voltage of the OLED is too high and the power efficiency is reduced. However, in the active matrix organic light emitting diode (AMOLED), the problems are well solved by progressively scanning input OLED current line by line.
In AMOLED devices, pixel circuits formed with polysilicon thin film transistors are usually used to provide current for the OLED device. Compared with amorphous silicon thin film transistors, polysilicon thin film transistors have higher mobility and more stable characteristics. Accordingly, they are more suitable for AMOLED displays. However, due to the limitation of the crystallization process, the polysilicon thin film transistors made on a large glass substrate usually have heterogeneity in electrical parameters such as threshold voltage and mobility, and the heterogeneity may lead to differences in the current and brightness of the OLED display device.
In addition, in the application of large size displays, due to the resistance of the power line for the backplane and the fact that drive current for all the pixel units is supplied by the same power line, the supply voltage in a region closer to the power supply is higher than that in regions farther from the power supply in the backplane. This phenomenon is called IR Drop.
Given the correlation of the current with the supply voltage, the IR Drop may also cause current differences in different regions, and accordingly the OLED display devices in different regions have different brightness.
In the related art, a variety of technical solutions are utilized to solve the problem of brightness differences in the OLED display devices. For example, a South Korea patent application No. 1020100102872 disclosed a pixel compensation circuit. However, there are still many problems in the existing technical solutions, such as a large number of signal lines and complex peripheral drive circuits.